PB2104: SOLUBLE B-CELL MATURATION ANTIGEN AS A MONITORING MARKER FOR MULTIPLE MYELOMA

Topic: 14. Myeloma and other monoclonal gammopathies - Clinical Background: Response to treatment in multiple myeloma (MM) is routinely measured by serum and urine M-protein and free light chain (FLC), as described by the International Myeloma Working Group (IMWG) consensus statement. A non-negligible subgroup of patients however present without measurable biomarkers, others become oligo- or non-secretory during recurrent relapses. Aims: The aim of our research was to evaluate soluble B-cell maturation antigen (sBCMA) as a monitoring marker measured concurrently with the standard monitoring in MM patients at diagnosis, at relapse and during follow up, in order to establish its potential usefulness in oligo- and non-secretory disease. Methods: sBCMA levels were measured in 149 patients treated for plasma cell dyscrasia (3 monoclonal gammopathy of unknown significance, 5 smouldering MM, 7 plasmacytoma, 8 AL amyloidosis and 126 classic MM) and 16 control subjects using a commercial ELISA kit. In 43 newly diagnosed patients sBCMA levels were measured at multiple time points during treatment and compared to conventional IMWG response and progression free survival (PFS). Results: sBCMA levels among control subjects were significantly lower than among newly diagnosed or relapsed MM patients [21.7 (18.5-24.9) ng/ml vs. 829.1 (665.3-992.7) and 543.2 (451.6-634.9) ng/ml respectively]. Significant correlations were found between sBCMA and the degree of bone marrow plasma cell infiltration. Out of the 37 newly diagnosed patients who have reached partial response or better per IMWG criteria, 33 (89%) have had at least a 50% drop in sBCMA level by therapy week 4. Cohorts of newly diagnosed patients made similarly to IMWG response criteria – achieving a 50% or 90% drop in sBCMA levels compared to the level at diagnosis – had statistically significant differences in PFS (Figure 1). Summary/Conclusion: Our results confirmed that sBCMA levels are prognostic at important decision points in myeloma. Importantly, the percentage of BCMA change is predictive for PFS. This highlights the great potential use of sBCMA in oligo- and non-secretory myeloma.Keywords: Multiple myeloma